Cassini images throw light on Saturnian moon

Kate Taylor, 21st June 2011

NASA's Cassini spacecraft has made its second-closest visit to Saturn's icy moon Helene, snapping details of its Saturn-facing side.

Cassini flew within 4,330 miles of the moon's surface, passing from its night side to its sunlit side. While the spacecraft made an even closer pass in March last year, flying within within 1,131 miles of the surface, the Saturn-facing side was at the time only illuminated by sunlight reflected from Saturn.

The latest flyby will give scientists the data they need to finish creating a global map of Helene. Because it's so small, it lacks enough of a gravitation field to pull it into a spherical shape.

Its two sides are very different, with one fairly smooth and appearing to be covered in dust and the other being far more rugged and marked with craters and gullies. Scientists don't really know why, and hope to get a closer look at these gullies, which may be the remnants of landslides.

Helene, which measures just 22 by 20 by 19 miles, is one of the smaller Saturnian moons - there are over 60 altogether.

It orbits Saturn at a distance of around 234,500 miles. It's particularly interesting as it is a so-called Trojan moon, sharing an orbit with the much larger moon Dione and the tiny Polydeuces, all 60 degrees apart. It's one of four Trojan moons in the saturnian system.